Question 1

Because they all involve formation of iron in cores of massive stars,all type II supernovae are equally luminous.

Accepted Answer

Type II supernovae have varying luminosities depending on factors such as the mass and composition of the star, as well as the energy released during the explosion.

Question 2

Because they all involve the detonation of a carbon-rich white dwarf at Chandrasekhar's limit,all type I supernovae are equally luminous.

Accepted Answer

Type I supernovae, specifically Type Ia supernovae, occur when a white dwarf star reaches a critical mass known as Chandrasekhar's limit and undergoes a runaway nuclear explosion. Because the conditions for these explosions are consistent, all Type Ia supernovae are believed to have roughly the same luminosity.

Question 3

Type II supernovae have little hydrogen in their spectra; it had been used up already.

Accepted Answer

Type II supernovae show prominent hydrogen lines in their spectra, indicating that they have not used up their hydrogen. This is a characteristic feature distinguishing them from Type I supernovae, which lack hydrogen lines.

Question 4

It takes less and less time to fuse heavier and heavier elements inside a high mass star.

Accepted Answer

This is because as a star's core becomes denser and hotter, the pressure and temperature needed for fusion reactions to occur decrease, allowing heavier elements to fuse at a faster rate.

Question 5

A carbon-detonation supernova starts out as a white dwarf in a close binary system.

Accepted Answer

A carbon-detonation supernova occurs when a white dwarf in a binary system accretes material from a companion star, eventually reaching a critical mass and temperature that triggers a runaway fusion reaction of carbon.

Question 6

Iron nuclei are the most tightly bound nuclei,which is why their production leads to type II supernovae.

Accepted Answer

Iron nuclei have the highest binding energy per nucleon, which means it takes more energy to break them apart into their individual nucleons. This makes the production of iron nuclei a key factor in the energy balance of a star. When a massive star runs out of fuel and can no longer generate enough energy to counteract the force of gravity, it collapses in on itself and triggers a type II supernova. During this supernova, the star's core becomes hot and dense enough to fuse lighter elements into heavier ones, including iron. This process releases energy and causes the star to explode.

Question 7

Once carbon is formed in massive star cores,the majority of nuclei formed from then on will belong to even numbered elements,due to addition to more helium nuclei as alpha particles.

Accepted Answer

This is because in the process of helium burning, alpha particles combine to form heavier elements in multiples of four (such as carbon-12, oxygen-16, etc.), which are even numbered elements.

Question 8

Two isotopes of the same element differ only in the number of protons.

Accepted Answer

Two isotopes of the same element have the same number of protons, but differ in the number of neutrons.

Question 9

Stellar nucleosynthesis is responsible for the existence of all elements except hydrogen.

Accepted Answer

Stellar nucleosynthesis is responsible for the creation of all elements heavier than hydrogen, but not for the existence of hydrogen itself. Hydrogen is believed to have formed during the Big Bang.

Question 10

A Type I supernova involves the collapsing core of a high mass star.

Accepted Answer

A Type I supernova typically involves a binary system where a white dwarf star accretes matter from its companion until it reaches a critical mass and undergoes a thermonuclear explosion, not the collapsing core of a high mass star.

Question 11

Novae are more closely related to type II than to type I supernovae.

Accepted Answer

Novae are caused by the accretion of material onto a white dwarf from a companion star, while type II supernovae result from the collapse of massive stars. Type I supernovae, like novae, involve white dwarfs, but in a different context.

Question 12

A recurring nova could eventually explode as a Type I supernova.

Accepted Answer

A recurring nova occurs when a white dwarf in a binary system accretes material from its companion star, triggering a thermonuclear explosion on its surface. While the white dwarf survives each explosion, over time it may accumulate mass until it reaches a critical limit and undergoes a final, cataclysmic explosion known as a Type I supernova. Therefore, a recurring nova has the potential to eventually lead to a Type I supernova.

Question 13

Most of the energy released during a supernova is emitted as neutrinos.

Accepted Answer

During a supernova, a large amount of energy is released in the form of neutrinos, which interact very weakly with matter and can pass through even the densest materials. It is estimated that as much as 99% of the energy released during a supernova is emitted as neutrinos.

Question 14

A massive star can fuse only up to the element silicon in its core.

Accepted Answer

A massive star can fuse elements in its core all the way up to iron, not just up to silicon. Beyond silicon, it fuses into elements such as sulfur, argon, calcium, and finally iron, at which point further fusion consumes more energy than it releases, leading to the star's collapse.

Question 15

The spectra of the youngest stars show the most heavy elements present.

Accepted Answer

The heavy elements in the universe were formed by the nuclear fusion processes that occur in stars. As new stars form from the remnants of previous stars, they inherit the heavy elements produced by their predecessors. Therefore, the youngest stars have the most heavy elements present in their spectra.

Question 16

Unlike supernovae,novae can explode more than once,increasing their luminosity by thousands of times.

Accepted Answer

Novae are recurrent explosions that can occur multiple times, unlike supernovae which are usually a one-time event. During a nova explosion, the brightness of the star can increase by thousands of times before gradually fading back to its original brightness over a period of weeks or months.

Question 17

Iron is the most stably bonded atomic nucleus.

Accepted Answer

Iron-56 is the most stably bonded atomic nucleus. It has the lowest energy per nucleon, which means it releases less energy when undergoing nuclear fusion or fission reactions. This stability is what makes iron a common endpoint for nuclear reactions in stars.

Question 18

The final core collapse of a massive star takes about 13 seconds.

Accepted Answer

The final core collapse of a massive star typically takes only a few milliseconds to a couple of seconds.

Question 19

Except for hydrogen and most of the helium,all the elements have been formed through stellar nucleosynthesis.

Accepted Answer

Stellar nucleosynthesis is the process in which new elements are formed through fusion reactions in the cores of stars. This process is responsible for the formation of all elements heavier than hydrogen and helium.

Question 20

Novae always occur in a close binary star system.

Accepted Answer

Novae occur in close binary star systems where one star is a white dwarf and the other is typically a main sequence star. As matter from the main sequence star falls onto the white dwarf, it can trigger a runaway nuclear reaction that causes a sudden increase in brightness, resulting in a nova.

Quiz 21: Stellar Explosions: Novae,Supernovae,and the Formation of the Elements